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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/54089] [SH] Refactor shift patterns
Date: Tue, 17 Dec 2013 11:11:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54089

--- Comment #30 from Oleg Endo <olegendo at gcc dot gnu.org> ---
A case from libmpeg2/slice.c:

        mov.b   @(1,r10),r0    // load of shift amount
        shld    r7,r6
        add     #1,r6
        extu.b  r0,r0          // zero extend shift amount
        shld    r0,r1          // r1 <<= r0
        mov     r1,r0

The zero extension of the shift amount variable could be omitted because shift
amounts > 31 are undefined behavior.  If the shift amount is in the valid range
of 0...31 the zero extension won't do anything.
A reduced test case:

int test33 (unsigned char* x, int y)
{
  return y << x[4];
}

results in:
        mov.b   @(4,r4),r0
        extu.b  r0,r0
        shld    r0,r5
        rts
        mov     r5,r0